The present invention relates to a signal measuring circuit and a signal measuring method used for the measuring circuit, and more particularly to a signal measuring circuit suitable for a measurement of a power supply noise generated by a large scale integrated circuit (LSI) and a signal measuring method used for the signal measuring circuit.
Recently, an operating speed of an LSI has been significantly increased. Accordingly, a power supply voltage or a grounding voltage tends to more easily vary and a high-frequency power supply noise tends to more easily occur in the LSI. This kind of power supply noise causes a failure of operation of a wireless device (degradation in reception quality, for example) or an abnormal operation of other electronic devices. In particular, in computers, the power supply noise caused by radiation of electromagnetic waves according to a cycle of the internal clock is increasing. The increase of power supply noise leads directly to a delay in signal propagation and adversely affects the operation of the LSI. In design for LSIs, it is important to precisely grasp the condition of the power supply noise. However, as described above, the frequency of the power supply noise is becoming higher. Thus, when observing the power supply noise from outside of the LSI, the high frequency component attenuates before reaching a point of observation. Therefore, it is difficult to make a precise measurement. Thus, in order to observe the power supply noise with high precision, it is essential that the power supply noise be observed inside the LSI. A related art of this kind is described in Ali Muhtaroglu, etc., Intel Corporation, Logic Technology Development, “On-Die Droop Detector for Analog Sensing of Power Supply Noise”, 2003 Symposium on VLSI Circuits Digest of Technical Papers.
FIGS. 10 and 11 are circuit diagrams showing electrical configurations of parts of a power supply noise measuring circuit described in above mentioned conventional art.
A reference unit shown in FIG. 10 has digital/analog (D/A) converters (DACs) 1 and 2, and a last stage 3 (NI-mirrors, FIG. 4 of Ali Muhtaroglu etc). The DAC 1 is used to calibrate an offset of a reference current caused by the process/voltage/temperature (PVT) condition and a mismatch between a positive reference current Iref+ and a negative reference current Iref−. The DAC 2 is used to program a voltage threshold suitable for detection of a variation in power supply voltage. The last stage 3 has a current mirror circuit for generating the positive and negative reference currents Iref+ and Iref−. The reference unit is designed to provide a measurement resolution of 10 to 20 mv, and the resolution varies depending on the setting of the DC voltage.
A detector module shown in FIG. 11 generates voltage thresholds vref1 and vref2 by use of the reference currents Iref+ and Iref− generated by the reference unit. Generally, in the power supply noise measuring circuit, the detector module receives the reference currents Iref+ and Iref− generated by the reference unit, detector module compares the voltage thresholds vref1 and vref2 with power supply potentials Vcc and Vss, and detector module outputs a result of comparison.
On page 4 and in FIG. 4 of Japanese Patent Laid-Open Hei No. 4-95,880, a related continuous high-frequency noise measuring apparatus is described. In the related continuous high-frequency noise measuring apparatus, first and second trigger controllers receive first and second trigger signals, respectively, after waiting a predetermined period of time. Thus, there is no need of increasing a processing speed of first and second counters and first and second comparators, so that the apparatus can be comprised inexpensively.
On page 3 and in FIG. 1 of Japanese Patent Laid-Open Hei No. 4-170,224, a related A/D converter is described. The related A/D converter generates a plural-bit digital signal register value in one clock cycle, so that the time for conversion of analog signal to digital signal is reduced by half or more.